In these years, digital video compression is applied more and more widely because of advances in technology of digital video compression and transition from analog recording to digital recording in the field of video compression. For video recoding media, DVDs and Blu-ray Discs (BDs) are used. For recording a video on a hard disk drive, the video is usually compressed using video compression techniques, such as the technique of the Moving Picture Experts Group (MPEG)-2 standard. These days, the technique of the H.264 (MPEG-4 AVC) is also used for video compression. At the same time, the techniques of the MPEG-4 and the H.264 are used as techniques for video compression in video shooting. Such techniques of the MPEG-4 and the H.264 are also used with home appliances such as digital video cameras and digital still cameras.
On the other hand, manufacturers differentiate their digital video cameras with new functions for video shooting in addition to normal photography, such as a mode for shooting in the dark. One of techniques for such new functions is a technique of high-speed photography. Video cameras which support high-speed photography (hereinafter referred to as high-speed photographic cameras) have already existed. However, such high-speed photographic cameras are expensive products because they tend to be costly due to pursuit of frame rates for shooting. Because of this, such high-speed photographic cameras have been used mainly in some specialized fields. Some specific techniques are used in order to incorporate techniques of high-speed photography into home appliances such as digital video cameras and digital still cameras. For example, one of the specific techniques is used for shooting videos with digital video cameras or digital still cameras at a frame rate lower than required for specialized fields. Owing to this, the cost for digital video cameras and digital still cameras are kept within the range of the cost adequate for home appliances.
Here is a flow of a signal in shooting a video using a digital video camera or a digital still camera. First, an image sensor having light-receiving elements, such as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor converts light to electricity. At this time, as light-receiving elements lack capability for color discrimination, a color filter is provided for each of the light-receiving elements in order to achieve color imaging.
Providing a color filter of three primary colors with each pixel would make the elements larger in size. Thus, the light-receiving elements of the image sensor are usually arranged in the Bayer arrangement. In the Bayer arrangement, each pixel is assigned one of the primary colors. FIG. 1 shows an example of the Bayer arrangement.
Signal data of colors of the light received by the light-receiving elements arranged in the Bayer arrangement is referred to as RAW data. A full-color image is generated by demosaicing the RAW data. Demosaicing is a process for converting RAW data of a pixel into data in RGB three primary colors by performing color interpolation using the RAW data of the pixel and pixels round the pixel (see Patent Reference 1, for example). RAW data may be converted not to data in RGB three primary colors but directly to YUV data in YUV format which is appropriate for video compression.
Since RAW data is used as a base data for interpolation, the RAW data of red, green, and blue has a large resolution in comparison with data of red, green, and blue after color interpolation, respectively. For example, data of red after color interpolation has a resolution of 8 bits, whereas RAW data of red has a resolution of 12 bits.
An image in RGB format after color interpolation or an image in YUV format (hereinafter referred to as a YUV image) is compressed as a video and then recorded on recording media. Reproduction apparatuses reproduce (or decode) the compressed video and convert it to in videos in image formats appropriate for display units (see Non-patent Reference 1).
In a high-speed photographic camera, processing time per frame for high-speed photography is so short that a period of time for processing RAW data outputted from an image sensor and compressing a video is very short. RAW data is processed in such a short period of time that the peak of power consumption per unit time is high. This requires reinforcement of power supply to support such a high peak of power consumption per unit time, resulting in increase in the cost for the high-speed photographic camera. The power of the high peak generates more heat and thus the high-speed photographic camera needs a countermeasure against the heat for the entire body.
Direct compression of RAW data, which will reduce processing load, may be counted as the countermeasure. Techniques for direct compression of RAW data are often used for shooting still images (see Patent References 2, 3). When coded data obtained by high-speed photography is reproduced, images are reproduced in slow motion. The period of time for processing RAW data per frame is longer for reproduction in slow motion than for high-speed photography. This will reduce the peak power.    [Patent Reference 1] Japanese Unexamined Patent Application Publication No. 2004-128583    [Patent Reference 2] Japanese Unexamined Patent Application Publication No. 2005-286415    [Patent Reference 3] Japanese Unexamined Patent Application Publication No. 2003-125209    [Non-patent Reference 1]“Kogashitsu MPEG-4 Hoshiki Digital Movie Camera” (Sanyo Denki Giho (Sanyo Technical Review) Vol. 37, No. 1, June 2005, the 76th volume of the set, P. 16)